The students _______ busily when Miss Brown went to get a book she _______ in t

题型：不详难度：来源：

The students _______ busily when Miss Brown went to get a book she _______ in the office.　

A．had written, left	B．were writing, has left
C．had written, had left	D．were writing, had left

答案

D。

解析

“把书忘在办公室”发生在“去取书”这一过去的动作之前，因此“忘了书”这一动作发生在过去的过去，用过去完成时。句中when表示的是时间的一点，表示在“同学们正忙于……”这一背景下，when所引导的动作发生。因此前一句应用过去进行时。